Traffic control system



Aug. 9, 1938.- D. WRIGHT 2,126,695

TRAFFIC CONTROL SYSTEM Filed April 28, 1954 5 Sheets-Sheet 2 K INVEN TOR. DEN/s WRIGHT 77M/NG DEV/CE. By

" M, 244W x A TTORNEYS.

D. WRIGHT Aug. 9, 1938.

TRAFFIC CONTROL SYSTEM Filed April 28, 1934 5 Sheets-Sheet 3 mr .m p m WW M Z N E M Y Patented Aug. 9, 1938 UNITED STATES PATENT OFFICE TRAFFIC CONTROL SYSTEM don, England Application April 28,

1934, Serial No. 722,893

In Great Britain May 19, 1933 7 Claims.

The present invention relates to traffic control systems for use at road junctions or the like and is more particularly concerned with systems 01 the type in which, inaddition to the signals for indicating go and stop, a caution signal is employed with is displayed between signal changes. The object of the invention is to control the display of the caution signal in such manner as to increase the factor of safety without causing undue delay at the crossing.

Though the invention is not limited to vehicleactuated systems and could be applied equally satisfactorily to fixed time controllers, the following discussion of its use in a vehicle-actuated system will make clearer its precise purpose. In such a system, use is made of contact-making pads let into the road surface and the arrangements are such that the passing of a vehicle over the pad when in receipt of the go signal ex- 20 tends the right ofv way for a period sufficient to ensure its safe passage over the crossing. For ordinary crossings the period allowed is generally of the order of eight seconds or somewhat less, and this has become known as the vehicle interval. A stream of vehicles following'each other at intervals of less than eight seconds would therefore extend the right of way up to a predetermined maximum period.

Considering now an isolated vehicle passing 30 over the crossing, it will be seen that the safe crossing period resolves itself into the sum of an eight-second vehicle interval plus for example a four-second amber or other warning period which precedes the signal change. On particularly wide crossings carrying a considerable volume of relatively slow moving trafiic, the minimum safe period which can be allowed is often in the neighborhood of sixteen to eighteen seconds and, with the ordinary method of working, to cater for this means an increase in either the vehicle interval or the cautionary period. A sufiicient increase in the vehicle interval is out of the ques tion, since it would seriously reduce the efliciency of the controller by allowing widely scattered trafiic to repeatedly run the controller up to the maximum period. An increase in the cautionary period is also undesirable'if it is to apply also to the traffic on the opposite phase which is awaiting the go signal.

The present invention overcomes the above objections by absorbing the additional time reconsecutively to the two phases or alternately no cautionary warning signal need be given to trafiic about to obtain right of way, the additional time required being absorbed in an all stop period which is also valuable as a pedestrian clearance period.

With these and other objects in mind, reference is had to the attached sheets of drawings illustrating one practical embodiment of the invention, and in which- Fig. 1 shows diagrammatically the layout of the system as applied to a trafiic intersection;

Fig. 2 is a circuit diagram of one form of trafllc control system embodying the invention;

Fig. 3 is an enlarged view. showing certain parts of the system of Fig. 2 which relate to the present invention;

1 Fig. 4 is a chart illustrating the position of the various circuit breakers which form a part of the operative control;

Fig. 5 is a plan view of a switch operating or timer mechanism;

Fig. 6 is an end view of the apparatus as shown in Fig. 5; and

Figs. '7 and 8 are transverse sectional views taken respectively along the lines 1-! and 8-8 and in the direction of the arrows as indicated in Fig. 5.

Referring primarily to Fig. 1, it will be seen that the invention has been illustrated in connection with a trafiic intersection involving lanes identified as A" Street and B Street. A unitarysignalling means I0 is provided in a position such that the signal indications will be visible to trafiic approaching the intersection over these lanes. In advance of the intersection and in each lane there are provided trafiic actuated elements II and I! which connect with a control or timer mechanism 13 by means of which the operation of the signalling means Ill is regulated.

This signalling meansas will hereinafter appear-includes for each traflic lane visual signal indications for the according of right of way, the interrupting of right of way, and for a cautionary indication. In accordance with common practice, these indications may be green, red, and amber, respectively. However, this is merely for the purpose of illustrating one preferred embodiment of the invention, and might be varied in accordance with local requirements either by way of consolidating or substituting another indication for the one prevailing in the present embodiment. Likewise, while the invention has been illustrated with a traflic control system at the point of intersection of two traific lanes, it

is obvious that the system might be enlarged or modified so as to control traffic on any number of lanes, and likewise the invention might be applied (as will hereinafter be apparent) to a fixed timer system.

Thus, referring to Fig. 2, it will be noted that the controls II and I2 have been shown in the nature of switches, and these switches are preferably of a pressure operated type such that, when trafllc mdves over them, a closing of the circuits controlled thereby will follow. A source of alternating electric current supply is connected to leads l4 and 81, and the first of these leads is extended and connected in parallel to the switches l i and I2. Extending from the switch I I is a lead it which connects with a relay ii, the latter controlling armatures I8 and IS. The latter arma- *ture is engageable with a contact coupled to a branch of lead l8, and the former, when in attracted position, engages a contact coupled to the branch i4.

I2 is connected to a lead 20, so that when the switch is closed, the relay 2i will be energized to attract armatures 22 and 23. The opposite side of the relay is coupled to a lead 24 interconnecting relays l1 and 2i and extending to the lead 61. Armature 22, when in attracted position, engages a contact extending from a branch of the lead i4, while armature 23, in a similar position, engages a contact associated with lead-20. 4

Now referring to Figs. 5 to 8, it will be noted that a timing apparatus is employed which may include an electromagnet 25 which serves to retract an armature 26. The latter has coupled to it a link 21, to the upper end of which a pawl 28 is secured. A stop 29 may limit the movements of this pawl in cooperating with the teeth of an annular ratchet 30. A return movement of this ratchet is prevented by a spring-pressed pawl 3i and the link 21 is pivotally connected to one end of a lever 32, the opposite end of which is spring retracted as at 33, and the body of which is rockingly mounted upon a shaft 34. Thus the armature 28 is normally maintained in projected condition incident to the spring 33, and upon being energized is retracted to cause the pawl 28 to override one tooth of the ratchet, this resulting upon deenergization of the electromagnet, in the pawl shifting upwardly under the influence of the spring 33, thus serving to rotate the ratchet 30 and the shaft 34, which latter, for this purpose, is afiixed to it. Arranged in the path of movement of the outer end of the lever 32 is a switch 35, which may include spring arms mounting contacts from which'leads 36 and 31 extend. As a consequence of this construction, it is obvious that include spring arms, mounting contacts and en gageable by the portions of the cams to close and open the switches during predetermined phases of a rotation of the shaft. At this time it will additionally be noted that the ratchet 30 may, for example, include eighteen teeth, and that each cam may have three operative portions for engagement, not alone with switches overlying the cam, but also underlying the same. In this manner, if,

Likewise, the second contact of switch for example, only six operative movements of the cam shaft are necessary to complete one cycle of the apparatus, it will not be necessary to rotate the shaft through 360 degrees, but instead a mere rotation of 120 degrees will suffice to complete the cycle. Thus the rotation of the cam shaft by a pawl and ratchet mechanism will present no dimculty, and also by arranging the switches and earns as shown, an extremely compact and unitary apparatus is presented, in which each camif desired-may operate any proper number of switches.

Now returning to a consideration of Fig. 2, it will be observed that certain of the cam operated switches have been identified as at 4| to 44 inclusive. With the parts in the positions shown in this figure, it is to be assumed-as will hereinafter he brought out-right of way exists in favor of "A Street" and is interrupted to traific traversing B Street". Thus a closing of switch ii causes an energization of relay ll, with a consequent attraction of armatures l3 and I3, and due to the fact that switch 4i is closed, it will be apparent that the attraction of armature l3 locks relay i! in, despite the fact that the switch II was only closed by, for example, the transition thereover of a vehicle. A series of resistances of diilerent values are identified at 41 to 32 inelusive, and a circuit through any one of these resistances may be closed from the D. C. supplying lead l5 through the condenser 33 to the common return lead i4 by a series of switches 54 to 33 inclusive. These switches are operated by the cams mounted upon the shaft 34, and thus various switches will be closed at different phases in the operating cycle. In the position illustrated switch 56 is closed, and thus current will be fed to the condenser 53. A flash tube 60 of the neon type is in series with a relay 6 l this tube being in shunt with the condenser 53 by having one of its terminals connected with a lead common to the condenser, the relay being connected through leads 62 and 63 with switch 42, which in the example given is closed, and thence through the armature IE to the lead H. The condenser 53 has a capacity in excess of the critical voltage of the tube 60. The value of the resistances 41 to 521s carefully apportioned to the tube and condenser characteristics so that, according to the resistance through which current is being fed to the condenser, different and properly timed intervals will elapse before the condenser voltage reaches a suiilcient point that the tube becomes conducting. Obviously, upon the operation of the tube 63 the relay M will function, so that its armature 53 will be energized to close the circuit through electromagnet 25 by virtue of the fact that this eleetromagnet has connected to it leads 64 and 65, and, of course, assuming that the latter leads are coupled (in a manner hereinafter brought out) with a source of electrical current supply. In this manner it will be obvious that each time the tube 80 flashes the cam shaft 34 will be advanced one position, to thus close or open certain of the switches 4i to 43 and 54 to l! inclusive.

,' At the present time the purpose of switch 33 ,will become apparent, in that it is arranged in shunt with the condenser 53, it being noted that a resistance 66 is preferably interposed in the lead 31 so that a non-sparking but short-circuiting path is provided for the condenser each time the electromagnet 25 is energized. As a consequence, any tendency of the condenser to retain part of its charge will be counteracted,

and each time this condenser reaches the critical voltage of the tube 6!] and causes the latter to become conducting the switch 35 will be closed to dissipate any residual charge of the condenser which might cause an improper functioning of the apparatus.

Reference is now had to Fig. 3 in which part of the structure specifically 'shown in Fig. 2 has been identified under the legend Timing device, it being observed, however, that the relay BI and the eiectromagnet 25 and also the signal elements, switches I58| and relays 82 and 83 are shown beyond such unit. These elements are also shown in Fig. 2 in connection with an embodiment of a traific actuated type of signal timing device. In this view the numeral 61 indicates one power supply lead, and 68 the second lead. The latter may be directly connected to signal elements 59 to 14 respectively, all of which form a part of the signal generally indicated at H]. The elements 69 may provide a right of way indication in favor of A Street, while element 12 may similarly provide for indication in favor of B Street. Elements and 73, respectively, may provide caution in'dications in favor of B and A Streets, while, finally, elements H and "I4 may provide for an indication of interruption of right of way to these two trailic lanes. Cam actuated switch elements of the nature shown in Figs. to 8 are identified by the reference numerals 15 to 80 inclusive, and it will additionally be observed that a similarly operated and constructed switch BI is furnished, the purpose of which will be hereinafter brought out. Moreover, relays 82 and 83 are provided, the first, when energized, serving to attract switches 84 to 89 inclusive, while the second controls the position of the switch 90. In connection with relays 82 and 83 it will be noted that they may be shunted by rectifiers 9! and have associated with them condensers 92 so as to operate in a satisfactory Inanner in connection with alternating current. Obviously, however, relays of a difierent type not requiring this associated structure may be employcd.

Attention is now invited to Fig. l, in which there has been charted the closed position of the several switch elements 4| to 46, 54 to 59, and T5 to Bil, the corresponding reference numerals having been applied adjacent the left hand edge on this chart. As will be noted, six positions are indicated in this chart, and this corresponds to the number of advances made by the shaft 34 before the latter completes one cycle. The heavy lines indicate a closed condition of the switches, the identifying numerals of which are arranged as afore stated.

The purpose of the foregoing construction and the cooperation of the parts will be best understood by considering the operation of the apparatus through one complete portion of a cycle.

With the parts in the position shown in Figs. 2

and 3, it is to be assumed that the shaft 34 occupies a position identified in the chart of Figure t under C. In this position, as will be clear from the chart, switch 15 is closed to energize the element 633, and thus accord right of way to A Street. Switch 71 is also closed to energize element 1! to interrupt right of way to B Street. Switch 8|, which is connected in circuit with the electromagnet 25 through armature-switch Bil and is in shunt with relay 82, is closed in all positions except those corresponding to the cautionary indication periods, i. e.,

positions A and D as shown in the shart of Fig. 4. so that except at these times relay 82 and therefore relay 83 cannot be energized. If it is now assumed that right of way is called from A Street to B Street by the passage of a vehicle over either of switches II or any equivalent operation of these trailic actuated controls, it will be obvious that, as aiore brought out, the tube 60 will flash so as to operate relay BI, which thereupon, by its armature-switch 63, energizes electromagnet 25. The shaft 34 is thus stepped into position D (Fig. 4) where switch 19 is closed to energize the signal element 13, while element 69 is de-energized incident to the opening of switch 15. In this position of the parts, however, switch 71 remains closed, and thereafter element ll of Street B" remains energized. This condition prevails until the expiration of the timing period (for example, four seconds), after which the relay 6| again operates so as to again close the circuit through electromagnet 25.

- Owing to the opening of switch 8| in position D,

the relay 82 may be energized and accordingly, upon the operation of the armature-switch 63, this relay operates in series with the electromagnet 25 and is of suiliciently high resistance to prevent the operation of the latter. This results in a discharge of the condenser 53 through tube 60 without operation of the electromagnet 25 and consequently movement of the camshaft out of position D does not occur and the cam operated switches remain unchanged in this position. However the condenser 53 begins to charge again. In the meantime relay 82 operates and attracts the armature-switch 89, thus providing a circuit for relay 83. Due to the attraction of armature-switches 8687, the element 13 is de-energized and element 10 is energized. During this interval armature-switch 88 is attracted to cause a simultaneous energization of elements H and 14, so that the indication interrupting right of way prevails. The effect on the signalling unit Ill, therefore, is that the cautionary indication of A Street is inoperative and. interruption to right of way only is indicated on this street, so that trafIic thereon is now stopped while on B Street the cautionary indication is displayed in addition to interruption of right of way. This prepares traffic in the latter street to restart. It will be noted that while relay 82 is energized and armautre-switch 63 is still closed, relay 83 is shunted by armatures 89 and 90, lead 64, coil of solenoid 25, lead 65, armature 63 and lead 68. When armatureswitch 63 is released thus interrupting this circuit shunting relay 83,relay 83 may be energized and operates in series with relay 82 and by means of the armature 90 again connects electromagnet 25 directly to the current supply. Since the cam shaft has not moved from position D during this sequence of operation, a further cautionary period is now timed (for example, four seconds),

.at the end of which energization of the electromagnet 25 occurs, which operates through armature-switch fill, to advance the cam shaft into position E. In this position the switch BI is again closed so that relays 32 and 83 are deenergized and element N is now energized directly through the switch 80 and the right of way indicating element 12 is energized by virtue of the fact that the switch 13 is closed. A similar sequence of operation takes place when the right of way is subsequently transferred from B Street to A Street and the circuit operations which take place will be readily followed from what has already been said.

As a consequence of this construction a double cautionary period is introduced between each change of signals, although the visible cautionary period to the respective streets is no greater than normal. If the arrangement is to be such that amber signals are given only to traflic losing the right of way, either one or both of switches TA and TB is opened and the operation of relay 8! will be effective in ale-energizing the cautionary indicating element as already explained, but the armature switches 85 and 81 which transfer the lighting circuit to the cautionary element of the other street will in each instance be left unconnected if the corresponding one of switches TA and TB is open.

Obviously the most common and in certain respects the most desirable method of signalling is that provided by means of colored lenses, lamps or reflectors, green lights, amber lights, and red lights, to respectively indicate right of way, caution, and interruption to right .of way. However, any desired substitute signalling arrangement might be provided. In addition, while in the present instance the cautionary phases or periods are equal, it is obvious that this need not necessarily be the case, and, as, afore brought out, while the present invention has been exempliiied in connection with a traffic controlled signalling system, it might equally well be employed in association with a fixed timing system.

The full details of the system which may be employed have, of course, not been shown in Fig. 2, in view of the fact that the vehicle actuated controls, minimum, re-setting, and maximum timing expedients, etc. already form the subject matter of patents such as British Patents 2 .040 and 355,741 for example. Thus, except in so far as hereinafter claimed, this portion of the system forms no part of the present invention, and is merely included to the extent shown for the purpose of exemplifying one operative form of apparatus. It is obvious where the present invention is included in a fixed time system, any desirable timer mechanism might be employed. If it should be desired to utilize substantially the same apparatus described in this specification, this might be done by simply eliminating the resistor O3 and permanently closing or shunting the switches ii and I2.

Regardless of the type of system in connection with which it is utilized, it will be understood that simply by the addition of, for example, switch II, the relays 82 and 83, as well as the structures associated therewith, an ordinary system may embody the benefits of the present invention, it being moreover apparent that numerous changes of construction and rearrangement of the parts might be resorted to without in any case departing from the spirit of the invention as defined by the claims.

In this connection it will be appreciated that although the embodiment of the invention illustrated in the drawings and described in the specification discloses a camshaft and cooperating cam contacts for controlling the signal circuits, and the term camshaft is used in the claims, the invention will be understood not to be limited to a camshaft type of construction but that a drum and contact segment or contact disk and brush type of construction or any other of the familiar types of cyclic circuit controlling devices could be employed without departing from. the spirit of the invention.

Having thus fully described the invention, what is claimed as new and desired to be protected by Letters Patent is:

1. In a signalling system having signalling circuits including signals adapted to display diiferent signal indications, a signal control apparatus comprising switches forming a part of said signalling circuits for operating said signals, a camshaft for operating said switches and having a plurality of positions thru which it is adapted to be operated cyclically, and time controlled means for normally operating said shaft from one position to another in its cycle at certain time periods so as to cause said switches to be operated to cause the display of such signal indications successively in a corresponding cycle, a relay in said system, means operated by said camshaft at a predetermined position in its cycle to operably connect said relay to said time controlled means for operation by the latter at completion of its time period at said position and so as to render said time controlled means ineffective to operate said shaft from said predetermined position, a switch operated by said relay and connected in series in one of said signalling circuits to cause when operated a change of signal indication from that which is caused by the operation of the signal control apparatus, and means operated by said relay to render said time controlled means again effective to normally operate said camshaft from said position on completion of a further time period.

2. In a signalling system having signalling circuits including signals adapted to display different signal indications, a signal control apparatus comprising switches in said signalling circuits for controlling the same, a camshaft for operating said switches and having a plurality of positions thru which it is adapted to be operated cyclically to provide a corresponding cycle of signal indications, means including a solenoid operative for driving said camshaft from one position of its cycle to another, and a timing device for normally operating said solenoid intermittently, a relay having a coil connected to said solenoid, means operated by said camshaft at a predetermined position in its cycle to cause operation of said relay by said timing device at said position and to render said solenoid ineffective to be operated by said device at said position, a switch operated by said relay and connected in series in one of said signalling circuits to cause when operated a change of signal indication, and

means controlled by said relay and said timing device for rendering said solenoid again effective to normally operate said camshaft after a time period of operation of said relay.

3. In a signalling system having. signalling means adapted to display different signal indications, a time controlled switching mechanism including switches adapted to be connected to said signalling means to operate the latter, a camshaft for operating said switches to so connect them successively to said signalling means and time controlled means for operating said camshaft cyclically to cause the display of said signal indications in a corresponding cycle, said system including a relay having a coil connected to said time controlled means to be energized thereby and having a switch operated by energization of said coil said switch being arranged in series with one of said first named switches and opened while said coil is energized to interrupt its connection to said signalling means, said relay when energized operatin its switch to cause a change of signal indication, and circuit means including a further switch operated cyclically by said camshaft and said circuit means in shunt across said relay coil normally to prevent such energization of the latter by the time controlled means except at certain points in its cycle at which the switch is open to permit such energizesaid switches and having a plurality of positions through which it is adapted to be operated cyclically to provide a corresponding cycle of signal indications, means including a solenoid operative for driving said camshaft from one position of its cycle to another, and a timing device for normally operating said solenoid intermittently, a relay having a coil connected to said solenoid, means operated by said camshaft at a predetermined position in its cycle to cause operation of said relay by said timing device at said position and to render said solenoid ineifective to be operated by said device at said position, and means controlled by said relay and said timing device for rendering said solenoid again effective to normally operate said camshaft after a time period of operation of said relay determined by said timing device.

5. In a signalling system having a plurality of circuits including signals for displaying difi'erent signal indications and a time controlled switching mechanism for energizing said circuits to operate said signals sequentially, said mechanism including switches in said signalling circuits, a camshaft for operating said switches sequentially and means including a solenoid for intermittently operating said cams it when intermittently energized, and a time controlled switch means connected to said solenoid for normally intermittently momentarily energizing said solenoid, said system including a relay having a coil in series with said solenoid and time controlled switch means, and a further switch means operated by said camshaft and connected to normally shunt said relay coil to prevent its energization and to render said solenoid effective to be energized by said time controlled switch means during a part of the cycle of said camshaft, said switch means being opened by operation of said camshaft in another part of its cycle to render said solenoid ineffective and to render said relay coil effective to be energized by said time controlled switch means, a switch means operated by said relay, a second relay operated by operation of said last named switch means, and a switch means operated-by said second relay to connect said solenoid to said time controlled switch means independently of the first relay so as to render said solenoid eifective to be again operated by the next intermittent operation of said time controlled switch means.

6. In a traiilc control system for interfering tramc lanes and having individual electric stop,

go and caution signals adapted to be energized to be displayed in said lanes for the control of traflic, a cyclic step by step switching device having a plurality of steps through which it is adapted to be operated to energize said signals to display the latter successively in said lanes, a timing device normally connected to said switching device for intermittently stepping said switch ing device at predetermined time periods to determine the time intervals of display of said indications, said switching device being arranged at one step in its cycle normally to display said caution signal to one of said lanes prior to the display of a stop signal in said one lane and of a go signal to another lane in the next step, and means including a relay arranged to be connected by said cyclic switching device at said one step in its cycle to render said timing device ineffective to operate said cyclic switching device and effective to operate said relay at the completion of the normal time period of said timing device in said one step, means operated by said relay to extinguish display of the caution signal in said one lane and to cause display of the caution signal to said another lane, and further means operated by said relay for rendering said timing device eilfective during the display of said last mentioned caution signal to step said switching device at the completion of its next timing period whereby said timing device is employed successively to time the two recited caution signal displays in one step of said cyclic switching device.

7. In a trafilc control system for interfering trailic lanes and having individual electric stop, go and caution signals adapted to be energized to be displayed in said lanes for the control of trafflc, a cyclic step-by-step switch device having a plurality of steps through which it is adapted to be operated'to energize said signals to display the latter successively in said lanes, a timing device normally connected to said switching device for intermittently stepping said switching device at predetermined time periods to determine the time intervals of display of said indications, said switching device being arranged at one step in its cycle normally to display said caution signal to one of said lanes following display of said go signal in said one lane in the preceding step and while a stop signal is being displayed to another lane, and means including a relay arranged to be connected by said cyclic switching device at said one step in its cycle to render said timing device ineffective to operate said cyclic switching Dams wisdom. I 

